Hi Ok, here's a BOM:
TI DAC8581 $1.85 each, two for 3.70 Linear LTC 2493 $2.95 TI LM4040C50 $0.36 Freescale MCF52254AF80 $4.38 Quad Op-amp $1.00 Misc resistors and caps $3.00 Other semi's $2.00 Total $17.39 at moderate volume prices. Depending on your shopping approach likely less than $20 how ever you do it. That gives you a CPU that's massive overkill (USB, Ethernet, 512K flash, 64K ram ...), a 4 channel ADC, a not so great reference, and dual 16 bit DAC's with pretty good performance. Spend a weekend writing code. Lay out a board the next weekend. fab it up and let it self train. Once you are done, you have a ~24 bit DAC with a 1 ppm or so INL. The linearity of your EFC is nowhere near 1 ppm, so INL isn't the measure you need to worry a lot about. Bob On Jun 29, 2010, at 9:01 PM, jimlux wrote: > Hal Murray wrote: >>> or with a pair of current output DACs and a resistive divider/summer so you >>> have a "high order" and "low order" voltage. >> If it were that simple, the manufacturers would package it up into a single >> chip. :) > > And they do... hence delta sigma designs.. > > Back in the good old days before big monolithic converters were available you > cold buy a fast wide DAC that basically was a hybrid with 2 smaller DACs and > a prom that was burned at the factory. > >> I think there are two areas of interest. One is the obvious one that steps >> on the high-order DAC won't cleanly map into a constant number of steps in >> the low-order DAC. > > Yep.. but if you're driving it from a CPU, memory is cheap... > >> The other is things like temperature shifts. You have to work out the specs >> for both paths and take the worst one. > > > It certainly isn't easy.. > > But, if you need something that isn't readily available off the shelf (for > one reason or another.. maybe you've got several thousand 8 bit DACs in your > garage that you're dying to use... along with a well regulated power supply > to run them all <grin>) > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
